Method and apparatus for mixing materials



April 8, 1952 c. B. CLOTWORTHY, JR

METHOD AND APPARATUS FOR MIXING MATERIALS Filed A ril zs, 1949 4Sheets-Sheet l INVENTOR C. B. CLOTMDRTHK JR.

BY I ATTORNEY April 1952 c. B. CLOTWORTHY, JR 2,592,245

METHOD AND APPARATUS FOR MIXING MATERIALS 4 Sheets-Sheet 2 Filed April25, 1949 lNl EN TOR 6.8 CLOTWORTHK JR ATTORNEY April 8, 1952 C. B.CLOTWORTHY, JR

METHOD AND APPARATUS FOR MIXING MATERIALS Filed April 25. 1949 4Sheets-Sheet 3 INVENTOR CB. CLOTWORTHK JR.

BY ATTORNEY A ril 8, 1952 c. B. CLOTWORTHY, JR 2,592,245

METHOD AND APPARATUS FOR MIXING MATERIALS Filed April 25, 1949 7 4Sheets-Sheet 4 lNl/ENT OR C. B. C L0 TWOR THKJR.

A 7' TORNE V Patented Apr. 8, 1952 Charles B. Clotworthy, J22,Brooklandville, Md.,

assignor to Western Electric Company, Incorporated, New York, N. Y., acorporation of New York Application Apr-i123, 1949, Serial No. 89,358

8 Claims.

This invention relates to methods of and apparatus for mixing materials,and more particularly to methods of and apparatus for mixing theingredients of plastic compounds.

Plasticizers and the like usually are added to plastic materials toimpart plasticity and other desirable properties to the materials. Inthe use of such materials it is usually desirable to have a continuousflow of the material rather than to supply the material in batches,wherein much handling and storage of the materials are required.Continuous mixing methods and apparatus have been known in the past, butthe proportions of the several ingredients mixed by these past knownmethods and apparatus have not been maintained uniform due to inabilityto continuously mix the ingredients in fixed proportions. Theingredients have been metered by the batch method, but then the mixingthereof has of necessity been very extensive and the amount of equipmentrequired was very large.

An object of the invention is to provide new and improved methods of andapparatus for mixing materials.

A further object of the invention is to provide new and improved methodsof and apparatus for continuously mixing and discharging ingredients ofa plastic compound.

A method illustrating certain features of the invention may includeadvancing a plurality of ingredients of a compound along a closed path,mixing the ingredients together as they are so advanced, supplyingunmixed ingredients into the closed path, withdrawing mixed ingredientsfrom the closed path in an amount low in proportion to the total amountof ingredients in said path and recirculating a large amount of theingredients in said path.

An apparatus illustrating certain features of the invention may includean endless chamber, means for introducing unmixed ingredients of thecomposition into the chamber at one portion thereof, means for advancingthe ingredients through the chamber, means for mixing the ingredientstogether as they are advanced through the chamber, and means forcontinuously withdrawing mixed ingredients from the chamber.

A complete understanding of the invention may be obtained from thefollowing detailed description of a method and apparatus formingspecific embodiments thereof, when read in conjunction with the appendeddrawings, in which:

Fig. 1 is a fragmentary, front elevation of a portion of an apparatusfor effecting one method embodying the invention;

Fig. 5 is a fragmentary, vertical section taken along line 5-5 of Fig.2;

Fig. 6 is a fragmentary, vertical section taken along line 6-6 of Fig.2;

Fig. '7 is a fragmentary, vertical section taken along line 'i-l of Fig.2;

Fig. 8 is a fragmentary, vertical section taken along line 8--8 of Fig.2;

Fig. 9 is a fragmentary, vertical section taken along line 2-9 of Fig.2, and

Fig. 10 is an enlarged, perspective view of a portion of the apparatus.

Referring now in detail to the drawings, there is shown an apparatus formixing the individual ingredients of a thermoplastic compound, such as,a compound consisting principally of polyvinyl chloride, a copolymer ofvinyl chloride and vinyl acetate, cellulose acetate, celluloseacetatebutyrate, or similar materials. The solid powdered constituentsof such a compound are placed in hoppers it, H and I2, which are largeenough to store substantial volumes of these ingredients.

The solid ingredients flow by gravity from the hoppers Iii, H and I2into the batch weighing devices l4, l5 and [6. One type of weighingdevice suitable for this purpose is disclosed and claimed in copendingapplication Serial No. 89,338 filed April 23, 1949, by H. R. Leypoldtand A. T. Stoddart, for Apparatus for Advancing Material.

The weighing devices l4, l5 and I6 may be controlled by a master controlsystem of a type similar to the control system shown in Patent 2,100,-874 to Ryan et al., and empty automatically and periodically into chutes20, 2] and 22, respectively, at the same time. The chutes 20 and 2!handling solid fillers, stabilizers, lubricants and pigments from thehoppers l0 and II are connected to a common discharge pipe 24 leadinginto a covered mixing cylinder 26 (Fig. 2), while the chute 22 leadsinto a covered mixing cylinder 28. The hopper l2 and the weighing deviceIt handle and dump dry, unplasticized, thermoplastic material inpowdered form into the cylinder 23.

A liquid plasticizer is stored in a tank 29 from which it flows into aweighing device 30. A pump 3! is driven by a motor 32, and pumps theliquid plasticizer from the weighing device 30 into the cylinder 28 atthe same time that the weighing devices l4, l and I6 discharge batchesof solid ingredients. The discharging action of the weighing devices It,I5 and I5 and 3!! begins simultaneously through the actuation of thecontrol system therefore so that the various ingredients dumped by theweighing devices are kept in fixed proportions. The weighing device 30and pump 3| supply the cylinder 28 with a plasticizer for thethermoplastic material at the same time that the thermoplastic materialis supplied to the cylinder 28 from the chute 22.

The material in the cylinder 28 is revolved therein by a U-shaped paddle40 (Fig. 2), which is rotated in a clockwise direction, as seen in Fig.2, at a rate of speed of 180 to 200 R. P. M. when the paddle is aboutinches in diameter, by an electric motor 42. The paddle 4a is providedwith two vertical blades 47-41 and with a conical central portion 48 fordeflecting material falling thereon outwardly toward the blades 41- 41.The plasticizer is sprayed onto the material in the cylinder 28 by anozzle 49 connected to the pump 3| (Fig. 1) by a pipe 55.

The blades 41-41 of the paddle 40 carry the powdered material therewitharound the cylinder 28, and push it toward the perimeter of thecylinder. Consequently, the material is kept spread out and continuouslymixed so that a large and continuously changing area of material isexposed to the droplets of plasticizer. As a result, the plasticizer isdistributed uniformly throughout all portions of the material.

The leading faces of the blades ll-41 slope backwardly and toward theperiphery of the cylinder 28 so that the material is free to slide offthe blades and to drop between the wall of the container and the outeredges of the blades. The blades repeatedly pick up the material, forcethe material outwardly and upwardly by centrifugal action, and drop thematerial so that the particles of material are continuously moved androlled. This mixing thoroughly and uniformly distributes the plasticizerinto the thermoplastic material.

The plasticized portion of the material is heavier than the dry portionthereof so that the plasticized portion is discharged continuouslythrough a tangential discharge chute 52 positioned near the bottom ofthe cylinder 28 and leading to a covered mixing cylinder 53, which isgenerally similar to the mixing cylinder 28. The chute is formed bycutting oblique communicating slots in the walls of the cylinders 23 and53. A paddle 55, which is similar to the paddle 40 and is driven in acounterclockwise direction, as viewed in Fig. 2, at the same rate ofspeed as the paddle d0, mixes the mixture of thermoplastic andplasticizer enterin the cylinder 53, and forces the material upwardlyalong the perimeter of the cylinder. The chute 52 is directed so thatits entrance faces generally opposite to the direction of movement ofthe paddle 40 as the-paddle approaches the chute 52 so that the materialis forced by the paddle therethrough. The exit of the chute 52 faces ingenerally the same direction as that of revolution of the paddle 55 sothat the paddle 55 does not push material into the chute 52.

The material is discharged continuously from the cylinder 53in'to acovered mixing cylinder 69 through tangentialdischarge chutes 58 and 59(Figs. 2 and 4) positioned near the tops and bottoms of the cylinders 53and 53 and directed so that they receive-the material being revolved inthe cylinder 53. Since the chutes 56 and 59 are positioned near the topand bottom of the cylinder 53, the average density of the materialsdischarged therethrough is the same as that of the average of the entireportion of the mixture in the cylinder 53. A paddle G2, which is similarto the paddles 40 and 55 and is revolved in a c10ckwise direction, asviewed in Fig. 2, at the same rate as the paddles 43 and 55, carries thematerial entering the cylinder 65 from the cylinder 53 around thecylinder 50 so that the ingredients of this material are mixed together.The chutes 5B and 59 extend in a direction with respect to therevolutions of the paddles 55 and 52 such as to receive material fromthe cylinder 53 and not receive it from the cylinder 60.

The material is forced outwardly and upward- 1y by the action of thepaddle 62, is repeatedly dropped and picked up, and is dischargedthrough top and bottom discharge chutes 64 and 65 (Fig. 5) facingopposite to the direction of rotation of the paddle 62. The materialdischarged through the chutes 64 and 65 into the cylinder 26 is pickedup by a paddle 68 revolved in a direction opposite to that of the paddle62. The paddle 68 which is of the same construction as the paddle 49,picks up the material and forces it upwardly and outwardly, and mixes itwith fillers and pigments discharged into the cylinder 26 by thedischarge pipe 24.

The material is discharged continuously from the cylinder 26 through topand bottom discharge chutes l0 and H (Figs. 2 and 6), which are directedso as to permit the force on the material in the cylinder 25 to move thematerial therethrough into a covered mixing cylinder 72. The material ismixed further in the cylinder 12 by a paddle 16, which is like thepaddle 40. The paddle 16 picks up the material, moves it outwardly andupwardly in a clockwise direction, as viewed in Fig. 2, and therebymixes it. This movement causes a substantial portion of the material tobe discharged continuously through top and bottom tangential chutes l8and 19 (Fig. 8) into the cylinder 53 for recycling, and the rest of thematerial to be discharged continuously through a top tangential exitchute 80. The material discharged tln'ough the chute has been thoroughlymixed and plasticized, and is suitable for use in various molding orextrusion operations.

The material discharged from the cylinder 12 into the cylinder 53 ismixed with the plasticized thermoplastic material entering the cylinder53 through the discharge chute 52 from the cylinder 28, and is high inproportion to the total quantity of the plasticized thermoplasticmaterial. Thus, the material entering the cylinder 53 through thedischarge chute 52 from the cylinder 28 is mixed with previously mixedmaterial, and any variation in proportions of the materials that may becaused by the operation of the batchmetering apparatus are eliminated asthe materials are cycled along the path described hereinabove. Likewise,any irregularity in the perform ance of any one or more of the mixingoperations is smoothed out by the recycling procedure. Heating coils6282 serve to heat the ingredients in the cylinders 25, 28, 53, 65 and72 during the mixing thereof.

The outer edges of the blades of the paddles 40, 55, 62, 68 and 16 aresufficiently far from the walls of the cylinders 28, 53, 60, 26 and 12,re-

spectively, to prevent the material from being caked on or wedgedagainst the walls of the cylinders, and are sufficiently close to thesewalls to insure that the paddles keep the material spread out thin andhigh on the heated walls.

Hence, the material is discharged continuously through the upperdischarge chutes as well as the lower discharge chutes, and isconstantly picked up and dropped in ach cylinder. A radial clearancebetween the edge of the blades and the walls of the cylinders ofabout'one-half of an inch has been found to be successful for mixingthermoplastic compounds including polymerized vinyl chloride.

The paddles effect a wiping action on the material so that it iscontinuously rolled and agitated. Inasmuch as there are no corners inthe side walls of the cylinders, there are no pockets to permitstagnation in the apparatus. Since the liquid plasticizer and thethermoplastic material are mixed thoroughly while in the mixing cylinder28, all the plasticizer is used to wet the pure thermoplastic materialand none is wasted on the ingredients added to the mixture in thecylinder 26. The total mixed material withdrawn for use during a givenperiod is equal to total unmixed ingredients added during that period,but a much larger mass is passing through the chambers.

For mixing some materials it may be desirable to introduce the materialsin a different order and to diiierent chambers than the order ofintroduction of and chambers to which thematerials described hereinaboveare introduced. This may be easily effected merely by changing thelocation of the discharge pipe 24 from the cylinder 28 to the one ofother cylinders desired. Or, introduction of the materials into severalof the chambers may be done.

The above-described method and apparatus for mixing materials serve tocontinuously discharge materials of unvarying proportions, even thoughbatch methods of supplying materials to the mixing apparatus are used.Hence, the batch weighing method can he used Without interfering withthe continuity and uniformity of the operation of the mixing apparatus.Obviously, the method and apparatus can be used with continuous meteringof materials thereto with excellent results.

What is claimed is:

1. The method of continuously mixing the ingredients of a plasticcompound, which comprises the steps of mixing measured amounts ofplastic material and a plasticizer, to form plasticized material,introducing the plasticized material continuously into an endless pathat a predetermined point therein, introducin into the path at a secondpoint therein measured amounts of solid ingredients to be mixed with theplasticized material, advancing the plasticized material and the solidingredients along the path, mixing the solid ingredients and theplasticized material as they are advanced along the path to form acompound, and withdrawing only a portion of the compound from the pathat a third poin therein.

2. The method of continuously mixing the ingredients of a plasticcompound, which comprises the steps of introducing periodically into achamber measured amounts of plastic material and a plasticizer, mixingthe plastic material and the plasticizer in the chamber to formplasticized material, introducing the plasticized material continuouslyinto an endless path at a predetermined point therein, introducingperiodically into the path at a second point therein measured amounts ofsolid ingredients to be mixed with the plastioized material, advancingthe plasticized material and the solid ingredients continuously alongthe path, mixing the solid ingredients and the plasticized materialcontinuously as they are advanced along the path to form a compound,heating the materials as they are mixed, and continuously withdrawingaportion of the compound from the path at a third point therein.

3. A mixer, which comprises a series of cylinders mounted intangentially contacting upright positions in which they form an endlesschain, a plurality of paddles mounted one for each in the cylinders forrevolution about the longitudinal axes of the cylinders, means forrevolving the paddles on said axes in directions such that each paddleis revolved in a direction opposite to that of the paddles in thecylinders immediately adjacent thereto, the cylinders havinginterconnecting slots therein of which each slot faces the paddle in oneof the cylinders in which the slot is formed as that paddle approachesthe slot and faces away from the paddle in the other cylinder as thatpaddle approaches the slot so that material in the first-mentionedcylinder is forced by the first-mentioned paddle through the slot and ispicked up by the other paddle, so that material is advanced fromcylinder to cylinder along the endless chain, a pro-mixing cylindermounted in tangential contact with one of the first-mentioned cylinders,the latter two cylinders having intercommunicating slots designed tofeed material from the Dre-mixing cylinder into the other cylinder, apaddle mounted rotatably in the pro-mixing cylinder, means for revolvingthe paddle in the pro-mixing cylinder in a direction such as to agitatematerial and force it through the last-mentioned slots, means for instroducing periodically unmixed materials into the pro-mixing cylinder,the cylinder from which material is discharged into the cylinder intowhich material is discharged from the pre-mixing cylinder having adischarge slot, and means for introducing periodically another materialinto one of the first-mentioned cylinders other than the cylinder havingthe discharge slot therein and other than the cylinder into which thepro-mixing cylinder discharges.

e. A mixer for powdered material, which comprises a cylindrical vessel,a second cylindrical vessel, said vessels being mounted on parallelvertical axes and in close relationship with one another, means forintroducing powdered mate'- rial into one of the vessels, a pair ofagitators mounted one for each in the vessels for revolution about thelongitudinal axes of the vessels, and means for rotating the agitatorsin opposite directions, said agitators being provided with bladessloping backwardly and toward the walls of the vessels as they arerevolved so that they tend to push powdered material in the vesselsagainst the walls of the vessels, the vessels being provided with anintercommunicating passage extending in a direction such that powderedmaterial is forced therethroug'h from the first-mentioned vessel to thesecond-mentioned vessel by movement of the material by the agitator inthe first-mentioned vessel and material is not forced from thesecond-mentioned vessel by movement of material therein by the agitatortherein, the blades of the agitators extending along the walls from thebottoms of the vessels substantially to the passage therein.

5. The method of continuously mixing the ingredients of a plasticcompound, which comprises the steps of mixing a batch of measuredamounts of plastic material and a plasticizer, periodically introducingthe plasticized material from the batch into an endless path,introducing into the path measured amounts of solid ingredients to bemixed with the plasticized material, advancing the plasticized materialand the solid ingredients together around the path a plurality of times,mixing the plasticized material and the ingredients as they are advancedalong the path to form a compound, continuously withdrawing compoundfrom the path, and controlling the periodic introduction of ingredientsto maintain constant proportions in the withdrawn composition.

6. A mixer, which comprises a closed upright cylindrical vessel having adischarge opening in the cylindrical wall thereof at a substantialdistance from the bottom of the vessel, means for introducing powderedmaterial in the upper portion of the vessel, a rotatable shaft mountedin alignment with the longitudinal axis of the vessel, means forrotating the shaft, and a generally L-shaped paddle connected to theshaft and revolved in the vessel thereby, one arm of the paddleextending along the bottom of the vessel from the central portionthereof for forcing powdered material on the bottom of the vessel towardthe cylindrical wall of the vessel and the other arm of the paddleextending along the 1 wall of the vessel from the bottom thereofsubstantially to the discharge opening in the cylindrical wall of thevessel, the last-mentioned arm of the paddle being substantiallyparallel to the longitudinal axis of the vessel, being spaced slightlyfrom the wall of the vessel and sloping opposite to the direction ofrotation, whereby substantially the entire mass of the powdered materialis moved by the paddle without packing the material between the paddleand the walls of the vessel.

7. An apparatus for incorporating a plasticizer into a powdered plasticmaterial, which comprises a closed upright cylindrical vessel having adischarge opening in the cylindrical wall thereof at a substantialdistance from the bottom of the vessel, means for introducing powderedplastic material into the upper portion of the vessel, a rotatable shaftmounted in alignment with the longitudinal axis of the vessel, means forrotating the shaft, a generally L-shaped paddle connected to the shaftand revolved in the vessel thereby, one arm of the paddle extendingalong the bottom of the vessel from the central portion thereof forforcing powdered material on the bottom of the vessel toward thecylindrical wall of the vessel and the other arm of the paddle extendingalong the wall of the vessel from the bottom thereof substantially tothe discharge opening in the cylindrical wall of the vessel, thelast-mentioned arm of the paddle being substantially parallel to thelongitudinal axis of the vessel, being spaced slightly apart from thewall of the vessel and the forward face thereof sloping backwardly fromthe inwardly positioned portion of that face to the outwardly positionedportion of the face as the paddle is revolved, whereby the powderedplastic material is mixed while being centrifugally urged toward and upthe cylindrical wall of the vessel to the discharge opening, and meansfor applying plasticizing material to the powdered plastic material onthe walls of the vessel.

8. An apparatus for incorporating a plasticizer into a powdered plasticmaterial, which comprises a closed upright cylindrical vessel having adischarge opening in the cylindrical wall thereof at a substantialdistance from the bottom of the vessel, means for introducing powderedplastic material into the upper portion of the vessel, a rotatable shaftmounted in alignment with the longitudinal axis of the vessel andextending through the bottom of the vessel, means for rotating theshaft, a generally L-shaped paddle connected to the shaft and revolvedin the vessel thereby, one arm of the paddle extending along the bottomof the vessel from the central portion thereof for forcing powderedmaterial on the bottom of the vessel toward the cylindrical wall of thevessel and the other arm of the paddle extending along the wall of thevessel from the bottom thereof substantially to the discharge opening inthe cylindrical wall of the vessel, the last-mentioned arm of the paddlebeing substantially parallel to the longitudinal axis of the vessel,being spaced slightly apart from the wall of the vessel and the forwardface thereof sloping backward from the inwardly positioned portion ofthat face to the outwardly positioned portion of that face as it isrevolved, a conical deflector mounted on and connected to the upper endof the shaft for guiding the powdered material toward the cylindricalwall of the vessel, and means positioned in the upper portion of thevessel for spraying liquid plasticizer toward the powdered plasticmaterial on the walls of the vessel.

CHARLES B. CLOTWORTHY, JR;

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 644,649 Walter Mar. 6, 1900682,292 Sukalle Sept. 10, 1901 808,599 Crichfield Dec. 26, 1905 882,925Boynton Mar. 24, 1908 1,605,596 Langelier Nov. 2, 1926 1,722,433Kirschbraum July 30, 1929 1,983,319 Simpson Dec. 4, 1934 2,005,950Moroney et a1 June 25, 1935 2,128,447 Wright Aug. 30, 1938 2,201,552Ahlmann May 21, 1940 2,263,790 Vermillion Nov. 25, 1941 2,498,125Knudsen et a1. Feb. 2, 1950

